External Recipients Not Receiving Email Messages Sent to a Distribution Group in Exchange Online (Microsoft 365)
Issue:
When users send email messages to a distribution group in Exchange Online (Microsoft 365) that includes external recipients, the external recipients do not receive the messages, and the senders do not receive non-delivery reports (NDRs).
Cause:
The issue arises due to the default configuration of distribution groups in Exchange Online. The ReportToManagerEnabled parameter is set to False and the ReportToOriginatorEnabled parameter is set to True. When both parameters are set to False, the Return-Path field in the message header is left blank (<>), which prevents the remote messaging system from sending emails / delivery reports to the sender who initially sent the message to the distribution group. Additionally, if spam filtering is enabled on the remote messaging system, messages with a blank Return-Path field may be flagged and dropped, resulting in the suppression of email delivery and reports.
Resolution:
To ensure external recipients receive messages and NDRs, follow the appropriate action based on your situation:
If the user is not sending the message as the distribution group:
If the sender's email address differs from the distribution group's email address, you need to enable the ReportToOriginatorEnabled parameter.
Execute the below PowerShell commands:
Command:
Install-Module -Name ExchangeOnlineManagement
Result:
Command:
Connect-ExchangeOnline
Result:
Make sure to replace the <group emailaddress> with the appropriate email address of the distribution group.
Command:
Set-DistributionGroup <group emailaddress> -ReportToOriginatorEnabled $true
Result:
To View the changes execute the below command.
Command:
Get-DistributionGroup <group emailaddress> | fl
Result:
If the user is sending the message as the distribution group:
If the sender's email address matches the distribution group's email address, you need to enable the ReportToManagerEnabled parameter.
Execute the below PowerShell commands:
Command:
Install-Module -Name ExchangeOnlineManagement
Result:
Command:
Connect-ExchangeOnline
Result:
Make sure to replace the <group emailaddress> with the appropriate email address of the distribution group.
Command:
Set-DistributionGroup <group emailaddress> -ReportToManagerEnabled $true
Result:
To View the changes execute the below command.
Command:
Get-DistributionGroup <group emailaddress> | fl
Result:
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